1. Technical Field
The present invention relates to a conductive pattern forming ink, a conductive pattern, and a wiring substrate.
2. Related Art
Ceramic circuit substrates are widely used as circuit substrates (wiring substrates) on which electronic components are mounted. The ceramic circuit substrates are substrates made of ceramic (ceramic-substrates) on which wiring lines made of metallic materials are provided. Such ceramic circuit substrates are advantageous in that internal components are formed in a multiple-layer manner and finished dimensions are stable because the ceramic constituting the substrates (ceramic substrates) is a multifunctional material.
The ceramic circuit substrates are manufactured as follows. A composition including metal particles is provided on a ceramic formed body made of a material containing ceramic particles and a binder in a pattern corresponding to wiring lines (conductive patterns) to be formed, and then the ceramic formed body to which the composition has been provided is degreased and fired in a sintering step.
As a method for forming a pattern on the ceramic formed body, screen printing is widely employed. The screen printing, however, is disadvantageous in that it is difficult to form fine wiring lines and achieve narrow pitches, and thus hardly satisfies the demand in recent years for highly densified circuit substrates with miniaturized wiring lines (e.g., wiring lines having a line width of 60 μm or less) having a narrow pitch.
Alternatively, a droplet discharge method, what is called an ink-jet method, has recently been proposed as a method for forming a pattern on a ceramic formed body. In the droplet discharge method, a liquid material (a conductive pattern forming ink) including metal particles is discharged from a liquid discharge head as droplets. For example, refer to JP-A-2007-84387.
In this regard, a related art conductive pattern forming ink has a problem in that conductive fine particles are separated out from the ink for forming a conductive pattern due to a volatilization of its dispersion medium around a droplet discharge portion of a droplet discharge head (ink-jet head) during a discharge waiting time and a long time continuing discharge. The deposited conductive fine particles around the droplet discharge portion cause changing the paths of discharged droplets, i.e., what is called a flight curve occurs, resulting in problems in that the droplets are hardly landed on a targeted portion and the discharge amount of the droplet is unstable. In addition, in this case, it is difficult that a pattern formed on a substrate by using the related art conductive pattern forming ink has a sufficiently uniformed thickness and width.
When a pattern is formed on a substrate by using the related art ink, cracks occur easily in the pattern in removing a dispersion medium from the formed pattern. As a result, disconnections occur easily in part of the formed conductive pattern. Particularly, such problems frequently occur along with the recent development of highly densified circuit substrates with miniaturized wiring lines having a narrow pitch.